1. Field of the Invention
This invention generally relates to a linear motion rolling contact guide unit, and, in particular, to a stability enhanced linear motion guide unit particular suitable for use as a linear motion guide unit of various machining tools and measuring devices.
2. Description of the Prior Art
A linear motion rolling contact guide unit is well known in the art and it generally includes a rail, a slider and a plurality of rolling members interposed between the rail and the slider. Such a linear motion guide unit is typically used in various machines and equipment, such as machining tools and measuring devices, for guiding a linear motion at high accuracy. FIG. 5 illustrates a typical prior art linear motion guide assembly including such a linear motion guide unit. As shown, the linear motion guide assembly includes a pair of rails 1 and 2 which extend straight and in parallel, two pairs of linear motion guide units, each pair including front and rear linear motion guide units 3 and 4, and a sliding table 5 which is fixedly mounted on the two pairs of linear motion guide units for supporting thereon any moving parts of machining tools or measuring devices.
As illustrated in FIG. 6, each of the linear motion guide units 3 and 4 has a basic structure which includes a rail A, which corresponds to rail 1 or 2 in FIG. 5, a slider B, which is generally U-shaped and thus is slidably mounted on the rail in a straddling fashion, and a plurality of rolling members C, or balls in the illustrated example. In the structure illustrated in FIG. 6, the rail A is generally rectangular in cross section and thus has a pair of opposite side surfaces, each of which is formed with an inner guide groove extending in parallel with the longitudinal axis of the rail A. In addition, the slider B is formed with a pair of endless circulating paths, each including a load path section, a return path section and a pair of curved connecting path sections connecting the corresponding ends of the load and return path sections, and the rolling members C are provided in the endless circulating paths to roll therealong endlessly. Each of the load path sections defines an outer guide groove located opposite to the corresponding inner guide groove of the rail.
In the structure shown in FIG. 6, balls are used as the rolling members C and each of the inner and outer guide grooves has a Gothic arch-shaped cross section so as to have an increased stability due to preloading and reliable and secure bearing of a load in all directions. On the other hand, use may be made of rollers as the rolling members C so as to obtain an increased stability against repetitively fluctuating loads and a prolonged servicelife.
In reality, various kinds of loads are applied to the sliding table 5 and thus to each of the sliders B in various directions, the linear motion rolling contact bearing assembly shown in FIG. 6 would not provide sufficient stability since only balls are used as rolling members C. It is thus conceivable to use both of balls and rollers as rolling members to obtain an increased stability in operation; however, a mere replacement of balls with rollers in one of the pair of endless circulating paths would not be enough because the characteristics differ between the endless circulating path including balls and the endless circulating path including rollers.